The present invention relates to an extruder incorporating a degree of-kneading adjusting device.
In general, two types of extruders are known and in practical use, one being a single-screw extruder and the other a twin-screw type extruder.
In one example of a conventional degree-of-kneading adjusting device, as disclosed by Japanese Unexamined Published Patent Application No. 5450/1975, a cut is formed in a part of the flight of the screw. An inserting member protruding into the interior surface of extruder barrel in which the screw is received is positioned in the cut thus formed, the gap between the end portion of the inserting member and the screw being thereby adjusted.
Also, in one example of a conventional degree-of-kneading adjusting device for a twin-screw type extruder, as described in Japanese Unexamined Published Patent Application No. 233408/1986, the gap between the slot of the screw and the slot of the cylinder is utilized to control the flow of raw material during operation, thereby to adjust the degree of kneading.
In the case of the conventional device of Application No. 233408/1986, it is also necessary to move the extruder barrel (or screw) in its entirety for the purpose of adjusting the gap between the slots. Accordingly, it is, for instance, necessary to position the entire barrel on the rails, as a result of which the extruder construction unavoidably becomes complexed and extruder component parts increase in number. In addition, the gap between the slots changes due to differences in the amount of expansion between the barrel and the screw due to variations in temperature. Therefore, with the conventional device, it is difficult to control the degree of kneading effectively.
On the other hand, the conventional device of Application No. 5450/1975 is free from the above-described difficulties; however, it is still disadvantageous in that its degree-of-kneading controlling performance is not sufficient. Specifically, even if the gap between the inserting member and the screw is adjusted suitably, some of the resin will flow through paths other than the gap, and therefore it is difficult to control the whole flow of the resin as intended. That is, it is difficult to adjust the degree of kneading to a desired value according to physical and temperature properties of the resin.